1. Field of the Invention
The present invention relates to a cooling system for an outboard motor arranged to supply outside water as a coolant pumped by a water pump to an engine and a transmission device.
2. Description of the Related Art
In conventional cooling systems for outboard motors, as disclosed in JP-B-3509171, a water pump is disposed in a vicinity of an upper surface of a lower case, and the water pump is driven by a drive shaft for transmitting the engine output to a propeller. A water intake is provided in a position below a waterline of the lower case. Outside water is introduced from the water intake, and then drawn into and discharged from the water pump when the water pump is driven. Thereafter, the water passes through a metallic coolant conduit member to rise into an upper case where it is supplied to an engine.
Recently, there have been developed outboard motors in which a transmission is located in a middle portion of a drive shaft to perform automatic speed changes and rotational direction switching of the drive shaft rotation, for example, as disclosed in WO 2007-007707.
A large number of devices such as a torque converter and a planetary gear mechanism are compactly installed in the transmission device. Therefore, the operating temperature tends to increase, and the temperature of lubricating oil stored in the transmission device increases due to the operating heat. This may result in degradation of the lubricating oil and further deterioration in the durability of the transmission device.